The present invention relates to a fluid damped unit which is particularly suitable for use as a shock absorber or telescopic strut, the unit including a cylinder, a piston rod inserted into the cylinder from one end of the cylinder through a guiding and sealing unit, a piston which is fastened to the piston rod inside the cylinder and which divides the interior of the cylinder into two work chambers, namely an annular work chamber bordering the guiding and sealing unit and a work chamber at that end of the cylinder which is located opposite the guiding and sealing unit.
The cylinder is charged with fluid, and the piston rod can be reciprocated between a fully retracted position at which the rod is telescoped within the cylinder to the extent possible and a fully extended position at which the rod is extended as much as possible out of the cylinder. A damper unit is located in the annular work chamber, this unit including a compression spring which surrounds the piston rod with one end facing toward the guiding and sealing unit and bearing against the guiding and sealing unit or against the cylinder.
A damping ring unit is arranged at the other end of the compression spring and divides the annular work chamber into two annular chamber sections. The damping ring unit includes a damping ring carrier, a damping ring arranged in the damping ring carrier to bear against the inner circumferential surface of the cylinder, and a stop which is movable together with the piston rod and which, starting at a predetermined intermediate position of the rod, abuts the damping ring carrier during movement of the piston rod from the fully retracted position in the direction toward the fully extended position, whereby the stop moves the damping ring carrier and the damping ring in the direction toward the guiding and sealing unit, so that hydraulic damping occurs, and the compression spring is compressed.
In accordance with pending U.S. patent application Ser. No. 008,513, filed Feb. 1, 1979, and assigned to the assignee of the present application, the damping ring unit is fixed in axial direction of the piston rod when the rod is retracted beyond the predetermined position, the damping ring bearing frictionally against the inner circumferential surface of the cylinder, the damping ring carrier being movable relative to the damping ring with only a slight axial play.
An object of the present invention is to provide a fluid damped unit arranged so that when the piston rod is retracted beyond its predetermined intermediate position, the damping unit is axially fixed relative to the cylinder in a position corresponding to the predetermined intermediate position of the piston rod, independently from the friction of the damping ring at the inner circumferential surface of the cylinder.
In accordance with the present invention, the damping ring unit is fixed in the axial direction of the cylinder when the piston rod is retracted in the cylinder beyond its predetermined intermediate position in the direction toward the fully retracted position,
(a) by fastening the damping ring carrier to the end of the compression spring which faces toward the carrier, and fastening the end of the compression spring facing toward the guiding and sealing unit to the guiding and sealing unit or the corresponding end of the cylinder; or
(b) by providing a stop on the cylinder and arranging the damping ring unit to bear against the stop.
The present invention ensures that, as the piston rod is extended out of the cylinder, damping of the rod movement begins with certainty exactly at the predetermined intermediate position of the piston rod.
As already provided in pending application Ser. No. 008,513, the damping ring unit may be bridged by means of a fluid passage which includes a valve mechanism responsive to the direction of movement of the piston rod in such a manner that the cross section of the fluid passage is smaller when the piston rod is extended in the direction toward its fully extended position than during retraction of the piston rod in the direction toward its fully retracted position. To form the valve mechanism, the damping ring may be axially movable relative to the damping ring carrier between two end positions, namely a first end position near the guiding and sealing unit and a second end position remote from the guiding and sealing unit. The damping ring assumes its first end position in which the cross section of the passage is larger when the piston rod is retracted in the direction toward its fully retracted position, and assumes its second end position in which the cross section of the passage is smaller when the piston rod is extended.
The valve mechanism essentially avoids damping of retracting movement of the rod by means of the damping ring unit when the piston rod is retracted, but effects significant additional damping of the piston rod movement, which damping can be made to vary along the travel path of the rod, beginning at the predetermined intermediate position of the rod in the direction toward its fully extended position.
Further, a damping ring of plastics material can be produced inexpensively, and the danger of scoring the inner circumferential surface of the cylinder is avoided when such a damping ring is used.
The damping ring carrier may consist of a metallic or a plastics material, and the sensitive damping ring is kept free of mechanical loading by protecting it by way of the damping ring carrier which absorbs such loading.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated and described preferred embodiments of the invention .